Techniques of constructing a network from multiple wirelessly connectable communications nodes are conventionally known. For example, in a known technique, when a packet is sent from a source node to a destination node through a predetermined communication path, a communication path is set for the respective nodes having the smallest and the largest hop count from the source node, among intermediate nodes on the predetermined communication path (see, e.g., Japanese Laid-Open Patent Publication No. 2006-94527). For example, when multiple wirelessly connectable nodes are disposed, neighboring nodes are detected to form clusters and neighboring clusters are connected to construct a network in a known technique (see, e.g., Japanese Laid-Open Patent Publication No. 2007-36361). For example, when multiple nodes are grouped into clusters and multiple wireless links are connected to the multiple nodes, a route from a source node to a target node is determined in a known technique (see, e.g., Published Japanese-Translation of PCT Application, Publication No. 2005-524337).
For example, in a network of wirelessly communicating sensors, two sensors, a first and a second reference sensor, at preliminarily known positions are used for measuring a sensor position of a third object sensor based on information of distances from the two reference sensors in a known technique (see, e.g., Japanese Laid-Open Patent Publication No. 2009-250627).
Nonetheless, when some of the arranged communications nodes are used as redundant nodes not included in a network, non-uniform distribution of the redundant nodes causes a problem of inability to improve the reliability of the network.